I would like to have a my one and only felony expunged.

This is relatively easy.  Its called a 1203.4 motion.In many counties either the Public Defender's office or the Probation Department will do it for free.  If that is not available any criminal defense attorney can do it.  It may take a couple of months but assuming that you are not on probation and you paid all of your fees and fines, it should not be difficult.  If you haven't paid your fines and fees talk to a lawyer anyway.

I'm not a California lawyer, but my research suggests that if the offense charged was possession for personal use, it may already have been automatically expunged.  You should talk to a local attorney about this, for reliable advice based on the details of your history.  Another good resource is the Self Help Center website within the California Courts' website, which has a broad discussion of expungment, and links to more specific information and forms.

Here's a link to a site that you may find to be of help:  http://www.courtinfo.ca.gov/selfhelp/other/crimlawclean.htm